Synthesis, structure, and reactivity of two families of rare-earth metal complexes containing discrete methyl cations [LnMe(2-x)(thf)n]((1+x)+) (x = 0, 1; thf = tetrahydrofuran) have been studied. As a synthetic equivalent for the elusive trimethyl complex [LnMe3], lithium methylates of the approximate composition [Li3LnMe6(thf)n] were prepared by treating rare-earth metal trichlorides [LnCl3(thf)n] with 6 equiv of methyllithium in diethyl ether. Heteronuclear complexes of the formula [Li3Ln2Me9L(n)] (Ln = Sc, Y, Tb; L = Et2O, thf) were isolated by crystallization from diethyl ether. Single crystal X-ray diffraction studies revealed a heterometallic aggregate of composition [Li3Ln2Me9(thf)n(Et2O)m] with a [LiLn2Me9](2-) core (Ln = Sc, Y, Tb). When tris(tetramethylaluminate) [Ln(AlMe4)3] (Ln = Y, Lu) was reacted with less than 1 equiv of [NR3H][BPh4], the dimethyl cations [LnMe2(thf)n][BPh4] were obtained. The coordination number as well as cis/trans isomer preference was studied by crystallographic and computational methods. Dicationic methyl complexes of the rare-earth metals of the formula [LnMe(thf)n][BAr4]2 (Ln = Sc, Y, La-Nd, Sm, Gd-Lu; Ar = Ph, C6H4F-4) were synthesized, by protonolysis of either the ate complex [Li3LnMe6(thf)n] (Ln = Sc, Y, Gd-Lu) or the tris(tetramethylaluminate) [Ln(AlMe4)3] (Ln = La-Nd, Sm, Dy, Gd) with ammonium borates [NR3H][BAr4] in thf. The number of coordinated thf ligands varied from n = 5 (Ln = Sc, Tm) to n = 6 (Ln = La, Y, Sm, Dy, Ho). The configuration of representative examples was determined by X-ray diffraction studies and confirmed by density-functional theory calculations. The highly polarized bonding between the methyl group and the rare-earth metal center results in the reactivity pattern dominated by the carbanionic character and the pronounced Lewis acidity: The dicationic methyl complex [YMe(thf)6](2+) inserted benzophenone as an electrophile to give the alkoxy complex [Y(OCMePh2)(thf)5](2+). Nucleophilic addition of the soft anion X(-) (X(-) = I(-), BH4(-)) led to the monocationic methyl complexes [YMe(X)(thf)5](+).

Monocationic bis-allyl complexes [Ln(eta(3)-C(3)H(5))(2)(thf)(3)](+)[B(C(6)X(5))(4)](-) (Ln = Y, La, Nd; X = H, F) and dicationic mono-allyl complexes of yttrium and the early lanthanides [Ln(eta(3)-C(3)H(5))(thf)(6)](2+)[BPh(4)](2)(-) (Ln = La, Nd) were prepared by protonolysis of the tris-allyl complexes [Ln(eta(3)-C(3)H(5))(3)(diox)] (Ln = Y, La, Ce, Pr, Nd, Sm; diox = 1,4-dioxane) isolated as a 1,4-dioxane-bridged dimer (Ln = Ce) or THF adducts [Ln(eta(3)-C(3)H(5))(3)(thf)(2)] (Ln = Ce, Pr). Allyl abstraction from the neutral tris-allyl complex by a Lewis acid, ER(3) (Al(CH(2)SiMe(3))(3), BPh(3)) gave the ion pair [Ln(eta(3)-C(3)H(5))(2)(thf)(3)](+)[ER(3)(eta(1)-CH(2)CH=CH(2))](-) (Ln = Y, La; ER(3) = Al(CH(2)SiMe(3))(3), BPh(3)). Benzophenone inserts into the La-C(allyl) bond of [La(eta(3)-C(3)H(5))(2)(thf)(3)](+)[BPh(4)](-) to form the alkoxy complex [La{OCPh(2)(CH(2)CH=CH(2))}(2)(thf)(3)](+)[BPh(4)](-). The monocationic half-sandwich complexes [Ln(eta(5)-C(5)Me(4)SiMe(3))(eta(3)-C(3)H(5))(thf)(2)](+)[B(C(6)X(5))(4)](-) (Ln = Y, La; X = H, F) were synthesized from the neutral precursors [Ln(eta(5)-C(5)Me(4)SiMe(3))(eta(3)-C(3)H(5))(2)(thf)] by protonolysis. For 1,3-butadiene polymerization catalysis, the yttrium-based systems were more active than the corresponding lanthanum or neodymium homologues, giving polybutadiene with approximately 90% 1,4-cis stereoselectivity.

Half‐sandwich rare‐earth metal tetramethylaluminate complexes [Ln(η5‐C5Me4SiMe3){(μ‐Me)2(AlMe2)}2] (Ln = Y, La, Nd, Sm, Gd, Lu) were obtained by reaction of the neutral homoleptic tetramethylaluminate complex [Ln{(μ‐Me)2(AlMe2)}3] with tetramethyl(trimethylsilyl)cyclopentadiene, (C5Me4H)SiMe3. Protonolysis reaction of the neutral mono(cyclopentadienyl) complexes with the Brønsted acid [NEt3H]+[BPh4]– in thf led to the formation of the monocationic methyl complexes [Ln(η5‐C5Me4SiMe3)Me(thf)3]+[BPh4]– (Ln = Y, La, Nd, Sm, Lu). Single‐crystal X‐ray diffraction study on the Y, Sm, and Lu derivatives showed a four‐legged piano‐stool configuration. Upon activation with [Ph3C]+[B(C6F5)4]–, the neutral half‐sandwich tetramethylaluminate complex [La(η5‐C5Me4SiMe3){(μ‐Me)2(AlMe2)}2] catalyzed the polymerization of butadiene in the presence of [AliBu3] to give trans‐1,4‐polybutadiene with narrow polydispersities (Mn/Mw = 1.05–1.09).(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Cationic, neutral, and anionic aluminum allyl compounds were synthesized, and their reactivity toward electrophiles was studied. The THF adduct of the previously elusive tris(allyl)aluminum, [Al(η 1 -C 3 H 5 ) 3 (THF)] (1), was isolated as an oil. Protonolysis of one allyl ligand in 1 using) contains a trigonal-bipyramidal aluminum center with both allyl ligands in the equatorial plane. The tetrakis-(allyl)aluminate K þ [Al(η 1 -C 3 H 5 ) 4 ] -(3) was also synthesized from the reaction of 1 with K(C 3 H 5 ). Reactions of the allyl compounds 1-3 with (i) benzophenone, (ii) allyl halides C 3 H 5 X (X = Cl, Br, I), and (iii) halogen X 2 (X = Br, I) showed considerable difference with respect to the ionic charge of the aluminum allyl. † Part of the Dietmar Seyferth Festschrift.

Rare-earth metal tris(borohydrides) [Ln(BH4)3(thf)3] (Ln = Y, La, Nd, Sm) are converted with one equivalent of the Brønsted acid [NEt3H]+[BPh4]- in thf into the monocationic bis(borohydride) complexes [Ln(BH4)2(thf)5]+[BPh4]-. They efficiently initiate the ring-opening polymerisation of epsilon-caprolactone.

Trimethylsilylmethyl complexes of the type [Ln(η5‐C5Me4CH2SiMe2NC6H4R‐4‐κN)(CH2SiMe3)(thf)n] containing a dianionic ligand [C5Me4CH2SiMe2NC6H4R‐4]2– with a para‐substituted anilido group and a CH2SiMe2 link were prepared. The yttrium complex [Y(η5‐C5Me4CH2SiMe2NPh‐κN)(CH2SiMe3)(thf)2] (2a) reacts with H2 to generate the corresponding dimeric hydride [Y(η5‐C5Me4CH2SiMe2NPh‐κN)(μ‐H)(thf)]2 (5a). Pyridine inserts into the Y–H bond in a 1,2‐fashion to afford the stable 2‐hydropyridyl complex [Y(η5‐C5Me4CH2SiMe2NPh‐κN)(η1‐NC5H6)(py)2] (6a). Upon reaction with tBuC≡CH, protonolysis takes place to give the dimeric alkynyl complex [Y(η5‐C5Me4CH2SiMe2NPh‐κN)(μ‐C≡CtBu)(thf)]2 (7a).(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

The alkyl abstraction reaction of [YR 3 (thf) -(E = Al, Ga, In) which dissociate to give the neutral compounds in apolar solvents such as benzene. Single-crystal

The trimethylsilylmethyl indium complex [In(CH2SiMe3)3] (1) was studied by single-crystal X-ray structure analysis at low temperature and shown to be weakly associated as dimeric units with a long indium−carbon bond in the bridges. The bis(trimethylsilylmethyl) cation [In(CH2SiMe3)2(THF)3][B(C6F5)4] (2) was prepared by protonolysis of the neutral complex [In(CH2SiMe3)3] with [NPhMe2H][B(C6F5)4] in THF. Crystal structure analysis revealed that mononuclear 2 adopts a square-pyramidal geometry.